Certain types of earth-moving and excavating machinery are equipped with digging buckets capable of holding anywhere from a fraction of a cubic yard to several cubic yards of material. One type of machine using a large digging bucket is called a walking dragline. Such draglines are often used in strip mining to remove "overburden" material covering, e.g., coal or ore, and to remove the product being mined. A large dragline may represent an investment of well over a million dollars; downtime is expensive, adds to the consumer cost of the product being mined and must be minimized.
Draglines are very large and include an enclosed machinery deck mounted on movable "legs" for machine transportability over a limited area. The machinery deck includes drive motors, cable reels, clutches and the like for manipulating a boom and boom-suspended bucket. The boom extends outward from the machinery deck by a distance of, for example, 300 feet or so. The digger bucket is attached to cables, one of which extends downward from the end of the boom to support the bucket weight. The other cable extends between the bucket and the machinery deck.
Digging is by lowering the bucket onto the material to be removed and dragging the bucket toward the machinery deck. As the bucket is drawn toward the machine, its digging teeth bite into the material as the bucket fills. After the bucket is filled, the boom is swung laterally and the bucket tipped for dumping the load. For a large dragline, the bucket capacity may be 80-90 cubic yards or even larger. And there are other types of machines, e.g., excavators, backhoes and the like, which use digger buckets mounted on articulated arms.
Because such digger buckets are subjected to severe use, often in hard mineral such as limestone, coal or rock, the bucket digging teeth wear or break and are arranged for replacement. A large bucket may have several tooth assemblies, the individual components of which are typically quite large.
In a conventionally-configured tooth assembly, the bucket includes a number of base noses protruding from the front, digging edge of the bucket. While such noses are intended to be a non-expendable, permanent part of the bucket, they sometimes break and replacement is required. Each such nose is fitted with a tooth holder and in a tooth assembly for a large bucket, such holder may be about 20 inches long (measured in the direction of digging) and weigh in excess of 450 pounds. A digging tip is attached to the holder and may have a length of 13 inches or so (as measured in the direction of digging), a width of about 12 inches and weigh about 160 pounds. Clearly, repair of such tooth assemblies is no trivial task. And during repair, the dragline is out of service for some period of time.
Conventional tooth assemblies are attended by certain disadvantages. One is that base noses, being of relatively small cross-sectional area, can break with annoying frequency. Since the base nose is a major component of the bucket per se, the resulting downtime can be enormously expensive.
Another problem with known tooth assemblies is that the tooth holder (interposed between the tip and the nose) also includes a nose piece which is subject to undue breakage. One reason is that a conventional tooth holder has an exposed surface which is sufficiently hard to reasonably withstand abrasive wear during digging. However, the holder must also be sufficiently ductile to withstand the rigors of digging without undue "brittle fracture." It is very difficult to make a holder with such inconsistent hard/ductile characteristics and, in fact, the exposed surfaces of the holder are of moderate hardness--unlike the high-hardness exposed surfaces of the tip. As a consequence, the exposed holder tends to wear at a disadvantageous rate. And for a particular size of tooth assembly, the holder itself is made of a large mass of metal and represents an item of significant cost. Still another problem is that the digging tip, intended to be replaced when worn, also includes a large mass of metal, a fact reflected in the costs of such tips.
An improved tooth assembly which is more resistant to breakage, which has a "beefier" base nose cross-sectional area for impact resistance, which is easier to manufacture and which has a tip of relatively small mass for easy replacement would be an important advance in the art.